Grandeur 

 Growth 



SCIENTIFIC SIDE-LIGHTS 



288 



eternity than in a new route opened to 

 commerce, a new sort of eatable, or a chemi- 

 cal discovery which may afterwards disturb 

 numerous interests. Thus, of the three ele- 

 ments which form the essence of man his 

 wants, his affections, and his intelligence 

 it is the last-named faculty which obtains 

 the preference. It is an advantage, es- 

 pecially to the young, to comprehend in 

 their totality truths the possession of which 

 does honor to the human mind. It is thus 

 that we learn to rise above the petty in- 

 terests of life, towards the higher regions 

 to which the divine patriotism of the soul 

 aspires. FLAMMARION Popular Astronomy, 

 bk. iii, ch. 7, p. 326. (A.) 



1399. GRAVITATION A MYSTERY 



A Mental Inference to Explain Phenomena. 

 Yet of the force of gravitation all we 

 know is that it is a force of attraction oper- 

 ating between all the particles of matter 

 in the exact measure which was ascertained 

 by Newton that is, " directly as the mass, 

 and inversely as the square of the distance." 

 This is the law. But it affords no sort of 

 explanation of itself. What is the cause 

 of this force what is its source what are 

 the media of its operation how is the exact 

 uniformity of its proportions maintained? 

 these are questions which it is impossible 

 not to ask, but which it is quite as impos- 

 sible to answer. Sir John Herschel, in 

 speaking of this force, has indicated in a 

 passing sentence a few questions out of 

 the many which arise. "-No matter," he 

 says, " from what ultimate causes the power 

 called gravitation originates be it a vir- 

 tue lodged in the sun as its receptacle, or 

 be it pressure from without, or the resultant 

 of many pressures, or solicitation of un- 

 known kinds, magnetic or electric, ethers or 

 impulses," etc., etc. How little we have as- 

 certained in this law, after all! Yet there 

 is an immense and an instinctive pleasure 

 in the contemplation of it. To analyze this 

 pleasure is as difficult as to analyze the 

 pleasure which the eye takes in beauty of 

 form, or the pleasure which the ear takes 

 in the harmonies of sound. ARGYLL Reign 

 of Law, ch. 2, p. 44. (Burt.) 



140O. 



A Statement of 



Conditions The Cause Still To Seek The 

 Falling of an Apple Not Yet Accounted For. 

 " Why does an apple fall to the ground ? " 

 is a question which has as great a signifi- 

 cance to us now as it had before Newton was 

 led, by pondering upon it, to the discovery 

 of the law of gravitation. For that law 

 only expresses the conditions of action of a 

 universal force tending to draw together all 

 masses of matter, while of the force itself 

 it gives no account whatever. We recognize 

 it by our own consciousness of effort in lift- 

 ing a weight from the ground; and this 

 recognition carries us from the sphere of 

 physical into that of moral causation. For, 

 as Sir John Herschel long ago pointed out, 

 our consciousness of direct personal causa- 



tion in the performance of a voluntary act 

 leads us to regard what we call the " Forces 

 of Nature " as the emanations of an all-per- 

 vading will, and those uniformities in their 

 action which we term her " laws " as the 

 manifestations of its unchanging continuity. 

 CARPENTER Nature and Man, lect. 15, p. 

 411. (A., 1889.) 



14O1. GRAVITATION A SIGN OF 



UNITY -Moves Whole Mechanism of Heavens. 

 There is one sign of unity which, of 

 itself, carries us very far indeed. It is the 

 sign given to us in the ties by which this 

 world of ours is bound to the other worlds 

 around it. There is no room for fancy 

 here. The truths which have been reached 

 in this matter have been reached by walk- 

 ing in the paths of rigorous demonstration. 

 This earth is part of the vast mechanism of 

 the heavens. The force, or forces, by which 

 that mechanism is governed are forces which 

 prevail not only in our own solar system, 

 but, as there is reason to believe, through 

 all space, and are determining, as astron- 

 omers tell us, the movement of our sun, 

 with all its planets, round some distant cen- 

 ter, of which we know neither the nature 

 nor the place. Moreover, these same forces 

 are equally prevailing on the surface of this 

 earth itself. The whole of its physical phe- 

 nomena are subject to the conditions which 

 they impose. ARGYLL Unity of Nature, ch. 

 1, p. 5. (Burt.) 



1 4O 2 . GRAVITATION ENABLES 

 BIRDS TO FLY Difference between a Bird 

 and a Balloon. It is remarkable that the 

 force which seems so adverse the force of 

 gravitation drawing down all bodies to the 

 earth is the very force which is the prin- 

 cipal one concerned in flight, and without 

 which flight would be impossible. It is 

 curious how completely this has been for- 

 gotten in almost all human attempts to 

 navigate the air. Birds are not lighter than 

 the air, but immensely heavier. If they 

 were lighter than the air they might float, 

 but they could not fly. This is the differ- 

 ence between a bird and a balloon. A bal- 

 loon rises because it is lighter than the air, 

 and floats upon it. Consequently it is in- 

 capable of being directed, because it pos- 

 sesses in itself no active force enabling it to 

 resist the currents of the air in which it is 

 immersed, and because, if it had such a 

 force, it would have no fulcrum, or resisting 

 medium against which to exert it. It be- 

 comes, as it were, part of the atmosphere, 

 and must go with it where it goes. No bird 

 is ever for an instant of time lighter than 

 the air in which it flies; but being, on the 

 contrary, always greatly heavier, it keeps 

 possession of a force capable of supplying 

 momentum, and therefore capable of over- 

 coming any lesser force, such as the ordi- 

 nary resistance of the atmosphere, and even 

 of heavy gales of wind. The law of gravi- 

 tation, therefore, is used in the flight of 

 birds as one of the most essential of the 



